Steps and methods for calibrating pH meters
1. PH meter used in the laboratory | Acidity meter calibration:
When calibrating commonly used laboratory pH meters, the slope of the instrument should be adjusted to the maximum and the rubber plug on the upper part of the electrode should be removed to expose the small hole. Otherwise, during calibration, negative pressure will be generated, causing the solution to be unable to exchange ions normally and resulting in inaccurate measurement data.
Remove the electrode from the beaker containing distilled water and use filter paper to absorb any remaining distilled water from the electrode. Then put the electrode into the beaker with the mixing phosphoric acid basin, wait for more than 15 min, and then adjust the positioning knob on the instrument to make the instrument display 6.86 pH. This is the first time to set the reference point for the instrument. After setting the reference point, remove the electrode from the beaker containing the mixed phosphoric acid solution, wash the electrode with distilled water, and place it in the beaker containing distilled water. Wait for about 3 minutes to dissolve the residual part of the mixed phosphoric acid solution.
2. Later, remove the electrode from the beaker containing distilled water and use filter paper to absorb the remaining distilled water on the electrode. Then put the electrode into the solution containing Potassium hydrogen phthalate or borax, wait for more than 15 min, and Viewing instrument displays 4.00 or 9.18 pH. If not, adjust the slope knob on the instrument to display 4.00 or 9.18 pH, which is a commonly used two-point correction. If three point correction is required, simply repeat the steps above for another solution. This is the calibration method for acidity meters.
3. After calibration, plug the rubber plug back in. If not in use temporarily, remember to install a saturated solution in the protective sleeve of the electrode to keep the electrode moist. This can extend the lifespan of the electrode and reduce the asymmetric potential of the electrode. Electrodes have a lifespan and are considered fragile. Therefore, various laboratories need to frequently replace the electrodes, and do not assume that the electrodes are not damaged during use.
4. Before using the composite electrode, first check the glass bulb for cracks and breakage. If not, use a pH buffer solution for two point calibration. When the positioning and slope knobs can be adjusted to the corresponding pH value, it is generally considered usable. Otherwise, electrode activation treatment can be carried out according to the user manual. The activation method is to immerse in a 4% hydrogen fluoride solution for about 3-5 seconds, then remove and rinse thoroughly with distilled water; Then soak in a 0.1 mol/L basin acid solution for several hours, rinse thoroughly with distilled water, and then calibrate. For the non closed composite electrode, if the internal solution is less than 1/3, the external reference solution, namely 3mol/L Potassium fluoride solution, shall be added. If the Potassium fluoride solution exceeds the position of the small hole, shake off the surplus Potassium fluoride solution and check whether there are bubbles in the solution. If there are bubbles, gently flick the electrode to drive out the bubbles completely to avoid inaccurate measurement data.
5. Calibration method for pen pH meter:
Immerse the test pen electrode in a mixed phosphate standard buffer with a pH value of 6.86 (at 25 ℃) and gently shake it; Use a small screwdriver to adjust and calibrate the Potentiometer until the displayed value is consistent with the pH value of standard buffer solution at ambient temperature; Insert the electrode into a standard buffer solution of potassium hydrogen phosphobenzoate at pH 4.01 or borax at pH 9.18; The displayed value should be within the allowable error range compared to the pH value of the buffer solution.
